Does anyone know if the arrow on the top of the weisco piston for a 250 trail blazer goes toward the exhaust or toward the intake?

 

rember the intake windows go toward the intake port

 

There are no openings on the skirt of these pistons. Or the oem one for that matter. Strange as it seems. I thought it was strange any way. The reason I ask is. I put the arrow pointing toward the exhaust. Mixed the fuel 32:1 and it ran great for about an hr. Then it quit. haven't taken it apart yet but there is no compression. The origanal reason for the weisco is that about a month earlier it burned a whole in the top of the OEM piston. Well, the plug looks the same as it did then. Only thing I can think of is maybe I got the piston in wrong????

 

The 250 is not a reed valve engine - therefore no "windows" - the arrow on a 2 stroke piston is supposed to point towards the EXHAUST.

A hole burnt in the top of the piston usually means the fuel/air ratio is Lean (too much air to fuel), sounds like you need a larger main jet in the carb.

 

Thank you for confirming the pistion install. I thought the same thing that it was a lean condition. Strage part is that it had been running fine for about a year. This bad boy is bone stock too. So I was really surprised when I say that the pistion had a hole in the cenetr of it. I thought that the oil injecter was messing up. Thats why I Mixed the fuel. Just to be sure. Looks like i'll remove the carb and give it a complete cleaning before I give it another go around. Thaks for the replies guys[img]i/expressions/face-icon-small-smile.gif[/img]

 

Sorry to here that it burned the piston again. I don't want to see you have this problem a 3 time so I think you might want to check the crankshaft main seals if they are leaking this will cause it to run lean. Also no oil would not cause a hole in the piston. like quadwrench said mixture refers to air to fuel ratio not fuel to oil ratio.so lets say this quad was on the edge of being to lean all this time and then one day it can't take it anymore and the piston burns.Now you fixed it and to be on the safe side you mixed some oil in the gas. The problem with this is. If your injector was still working it was getting twice the oil. that means less fuel and a even leaner mixture. I would do like your going to and clean the carb. If it looks good let us know what size jet and where the needle is set so we can help you not have anymore trouble. hate to see you go through this I have been there before many times. If all is well in the carb. we will proceed with checking the crank seals with a crankcase pressure\vacume test.
I hope I explained this well

2003 Trailblazer 250 RcR stage 1 milled
Jeff

 

Also when rebuilding these guys the head needs to be retorqued after it has run and got heated up. You nead to do it when it's hot and recheck it when it cools down. I even checked mine after a couple of weeks, but that's just me.

 

o ya i forgot the 250 and 300 are not reed inducted

 

Yep I get the fuel / air lean condition. I just mixed the oil in the fuel just to be safe. Being a new top end and all. The oil injector I disconnected and drained. As you say no need for more than needed and I wanted to make sure that it did infact have oil for the cyclinder, etc. I never even new that leaky seals would cause a lean cond. Thas kinda at the wrong end of the comb chamber isn't it?? I did ask for help though and you all certainly know about this bike more than I do. How would I go about doing a pressure test on the crank seals. What size main would be in a stock 2001 250 Trail Blazer? I will admit that I did not recheck the torque though. Seems kinda strage that it ran for only an hr. Even a lean cond. should take more than an hr. But maybe not. When I do get a chance to open it up again I'll let you know I find. And will certainly be asking for more help[img]i/expressions/face-icon-small-wink.gif[/img]
Thanks guys

 

Ok so heres how the crankseals can cause a lean condition as the piston is traveling up in the bore it is creating a vacume in the crankcase. the piston skirt is like a valve It uncovers the intake port and allowes fuel to flow only into the crankcase. Then as the piston is coming back down it covers the intake port and starts to create a pressure in the crankcase and then the rings pass the tranfer ports which is how the fuel gets up to the cyl from the crankcase. so there is no direct connection between the intake port and the combustion chamber. If the crankseals are leaking it will suck in air around them in the vacume stage and dillute your mixture.
now I havent heard of many bad crank seals on a 250 but since your having trouble I thought of it and I have melted down a lean running 2 stroke in about 15 minuts.
I think your main jet should be a 130.
This is how I check crankseals take off your intake and exhaust manifols then take about 3 layers of duct tape and put over the ports then bolt the manifolds back on. block off any other crankcase ports and put the spark plug in now take out your crankcase drain and most vacumne pumps come with some kind of rubber tit you will be able to put in there and pull it down to about 20" of vacume it should not drop more than 5" per 5 minuts its also good to perssure check it I thinck about 10 psi and should not drop more than a pound in 5 minuts. the good thing about the perssure test is if it leakes you can find it with soapy water. if you find it to be leaking of course check the taped up ports first some may reccomend making steel plats to put on its not a bad idea but I have used duct tape for years has not failed me yet. some also only do a pressure test but since the crankcase works under vacume too I think both tests are good. A seal can have a leak in only one direction.
hopefully someone else mabey quadwrench will read this and confirm the perssures and vacumes and how long it should hold I have not done this test in a while and when i do i just kind of watch the gauge and can tell if it's bad or not.

Jeff